Desulfurization of iron



1965 R. K. MATUSCHKOVITZ 3,l99,975

DESULFURIZATION OF IRON 2 Sheets-Sheet 'l Filed Oct. 30, 1962 INVENTOR.ATUSCHKOVITZ RICHARD K. M

ATTORNEYS Aug. 10, 1965 R. K. MATUSCHKOVITZ 3 DESULFURIZATION OF IRONFiled Oct. 30, 1962 2 Sheets-Sheet 2 FIG. 3

RICHARD K. MATUSCHKOVITZ ATTORNEYS IN VEN TOR.

United States Patent 35199375 DESULFURIZA'HON OF IRON Richard K.Matuschhovitz, Chicago, ill., assignor to Chemetron Corporation,Chicago, lil., a corporation of Deit-.Ware

Filed Oct. 39, 1962, Ser. No. 234,@20 3 Ciaims. (Ci. 75-43) Thisinvention relates to a method for reducing sulfur content of iron in acupola furnace. More particularly, this invention relates to a method ofrefining iron by the intermittent addition of calcium carbide in astream of inert gas injected below the surface of the molten iron in thecupola well during operation of the cupola.

Shaft furnaces, such as cupolas, have been used for the production ofcast iron by melting pig iron, scrap iron and steel with fiuxingmaterials, the heat being supplied by the combustion of coke with airblown into the cupola through tuyeres. In ordinary practice the cupolais first filled with coke to some distance above the tuyere level andthis coke is ignited and burnt in. When the coke is white hot, chargingbegins and the rnelting operation is started. Layers of limestone andpig iron and scrap iron and steel are placed above the coke bed withalternative layers of coke to replace the coke which burns out duringthe operation. As the iron charge descends in the cupola, the metalbecomes soft and finally rnelts in the melting zone which is the hottestzone immediately above the tuyere level. Lquid superheated iron fiowsaround the coke pieces in the coke bed and is collected in the Well ofthe cupola from where it is tapped through the tap hole.

The Carter Patent No. 2,643,185 discloses that the addition of arelatively small amount of calcium carbde to the cupola charge iseffective in reducing the sulfur content of the iron. The Timmerbeil etal. Patent No. 2,865,735 discloses an improvement whereby calciumcarbide whose melting point is lower than 1800 C. is introduced into thecupola as part of the charge. These techniques have produced substantialimprovements in the desulfurization of iron but they have certaininherent disadvantages, one of which is that the procedure is noteffective until several charges have been passed through the cupola.Furthermore, the calcium carbide reacts With the iron in the rneltingzone of the cupola and part of the calcium carbide is oxidized andcreates heat which increases the melting zone temperature, which resultsin a higher carbon pickup and higher rnelting rate. In addition, thecontact between the molten iron and the calcium carbide in the meltingzone .and above is somewhat ineicient with the result that the molteniron is not efficienly desulfurized.

It is the object of this invention to provide an efficient method fordesulturizng iron. It is a further object of this inven-tion to providea method for eiciently desulfurizing iron with calcium carbide which isimmediately effective with the first charge. These and other objects areapparent from and are achieved in accordance with the followingdsclosure.

In accordance with the present invention, it has been discovered thatiron can be efiiciently desulfurizcd by reaction with a stream of inertgas containing powdered calcium carbicle Suspended therein injected intothe molten metal in the Well of the cupola. The calcium carbide ispreferably introduced on an intermittent basis with short injectionperiods, generally less than one minute in duration. The calcium carbideis dispersed efectively throughout the molten metal in the vicinity ofthe inlet for the gas and calcium carbide into the cupola. The calciumcarbide is efliciently contacted with the molten metal and is highlyeffective in desulfurizing the iron. The reaction between the sulfur inthe molten metal and the calcium carbide takes place rapidly at thetemperature of the 'ice molten iron which has descended through theheating zone of the cupola and is at a temperature in the range of2650-3100 F. The procedure is effective in desulfurizing the firstcharge of iron meltcd in the cupola and continues throughout the entirecupola run. The procedure c'an be applied to intermittently tappedcupolas or continuously tapped cupol-as so long as the gas streamhearing the calcium carbide is introduced into the molten metal belowthe surface there'of.

The invention can perhaps be best understood by reference to theattached drawin'gs wherein:

FIG. l represents a cross sectional View of an intermittently tappedcupola provided with a gas injection tube for use in the operation ofthis invention;

FIG. 2 represents a cross sectional View of a calcium carbide injectiondevice; and

FIG. 3 represents a cross sectional View of the well of a continuouslytapped cupola arranged for operation 'of this invention.

Turning to FIG. l, a cupola furnace generally indicated by 10 isprovided With a supporting base 11 and legs 12. On the supporting base11 is `a cylindn'cal steel shell 13 which is lined with a refractoryacid or basic lining 14. On the supporting base 11 is a sand bottom 15which is inclined slightly toward the tap hole 16 from which molten ironis withdrawn over a refractory lip 17. As illustrated in FIG. 1, the taphole 16 is plugged with a clay plug 18. The cupola 10 is provided withtuyeres 20 conected to piping 21 leading to the annular tuyere box orwindbox 22 which surrounds the cupola. Near the top of the cupola is abucket 23 suitably supported from a crane (not shown) by a wire rope 24.The charging bucket 23 is adapted to move into and out of the cupola byway of an opening in the cupola Wall above the ch-arging floor 25. Asshown in FIG. 1 the cupola Zt) has a pool of molten iron 26 in thecupola well below the tuyeres 20. The cupola is charged with coke 27 andscrap iron 28. The heat of combustion of the coke in the air blastprovided by the tuyeres 20 .rnelts the iron scrap 28 and the molten irondescends the cupola to the molten iron pool 26. Near the bottom of thecupola above the sand bottom 15 there are one or more inlet ports 3@through par-t of the refractory lining 14. An inlet tube 31, preferablyof graphite or other refractory material, although steel tubing isadequate, is inserted through the steel shell 13 and part of therefractory lining 14, where it connects to the inlet port 30. It ispreferably fitted snugly to the steel shell 13 and cemented into therefractory lining with refractory cement.

T he inlet tube 31 is affixed to a rubber hose or other suitableflexible tubing 32 by means of a nipple or other fitting 33.

In the operation of this invention a stream of nitrogen or other inertgas is injected via the rubber hose 32, the nipple 33 :and the inlettube 31 and the port 30 into the molten metal beneath the surfacethereof. Powdered calcium carbide is injected into the gas streamintermittently and carricd with the gas stream into the molten metal 26.

FIG. 2 illustrates the calcium ca-rbide injection system which isconveniently used in this invention. It includes a hopper 35 in whichpowdere-d calcium carbde is stored. A supply of nitrogen or other inertgas under pressure is provided to the hopper 35 by way of a line 36which is equipped with a regulator valve 37 for adjusting the pressureof the gas stream within' the hopper 35. The supply of inert gas, underpressure of 50-100 pounds per square inch, is provided to the apparatusby a line 38 which has a T 39 connected to the line 36 to provide gas tothe hopper. The line 38 -proceeds beyond the T 39 through a pressurecontrol valve 40 t-o a venturi tube 41 which is disposed within a T 42at the bottom of the hopper 35. The bottom of the hopper 35 is connectedwith a conduit 45 equipped with a regulating valve 36 to control therate of flow of the powdered calcium carbide out of the hopper 35. Asthe .powdered calcium carbide enters the T 42, it is ent r ained in thestream of inert gas passing throug the venturi tube 41 and the stream ofgas and entrained calcium carbide passes out of the T 42 by way of theflexible tube 32 which connects with the inlet tube 31 and leads thestream of gas and calcium carbide into the cupola well below the surfaceof the molten metal.

FIG. 3 illustrates the invention as operated in a continuously tappedcupola St?. This cupola is supported on v a base 49 which is afxedtolegs 51 and contains a shell 52 provided with a reractory lining. A sandbottom 54 is packed firrnly on the cupola base 49 and is inclinedslightly to the tap hole 56, shown closed with a clay-plug 59, above there-fractory spout 57. The cupola is equipped with tuyeres 58 and inother respects is a complete cupola turnace. Inlet tubes se of graphiteor other refractory material are snugly fitted through the cupola shell52. .and

extend part way into the re-f ract-ory linin 53. They connect withp-or-ts 61 in the refractory lining which lead into the cupola well. Theports 61 are so ar-ranged as to be below the level or" the niolten iron-pool 62 which collects in the cupola well below the charge of coke 63and scrap iron dd. The stream of inert gas is passed con-tinuouslythrough the inlet tubes 60 'and the ports 61 into and beneath thesurface of the molten metal 62, and the powdered calcium carbide isinjected ntermittent ly into the stream of inert gas .and thus carriedinto the molten metal pool 62.

in the cupolas E@ and the inlet tubes 31. and se, respectively, are solocated that they terminate approximately 1 /2 to 2 inches from theinside of the refractory lining. 'Thus they are removed from the moltenmetal and are protected from disintegration under the temperature of theoperation. During the lining of the cupola before operation, the tubes31 and 6% which extend through the shell of the cupola are prefera-blyplugged with a cylindrical plug of approximately the same internaldiameter as the tubes 31 and 69. Then the lining is ap lied to theinside of the cupola to the thickness desired and the plugs are removedfrom the tubes 31 and 60, thereby providing inlet ports 3@ and 61. Theseports can also be prepared by applying refractory cement aroundcylindrical plugs in the tubes 31 and 6%. This is the preferred methodwhen part of the refractory lining has been eroded away during operationof the cupola.

The inert gas which is injected into the metal pool in the cupola can benitrogen or a monatomic gas such as argon or helium. In certain cases,it can be chlorine or mixtures of nitrogen and chlorine. The gas issupplied to i the calcium carbide dispensing unit as illustrated in FIG.

2 at a .pressure of 50-'100 p.s.i.g. The pressure of the inert gas inthe hopper 35 is preterably in the range of 5-10 pounds per square inch.The pressure of the gasstrearn as it enters the flexible ho se or tubing3?, is in the range of 15-40 pounds per square inch. Thispressure can beregulated in relation to the ferrostatic head within the cupola abovethe inlet port s 3@ or 61. The ferrostatic head can in some cases be 12to 15 inches. In such cases, gas pressures of 1540 p.s.i.g. .areadequate.

The stream of inert gas is continuously passed into the cupola via theinlet tubes 31 or 60 and the ports 3% or 61. This prevents plugging ofthe inlet ports with solidified iron -or with slug. The continuousstream of gas also has the advantageous efiect of cleaning the iron byfiushing out gases contained therein such as oxygen and hyd rogen andimproves the structure of the iron by causing oxides to float to thesurface where they are removed as slag. The gas stream has the eect ofchanging the surface'tension of the molten metal, which aids in theremoval of gases and slag. In addition, it has a benecial eifect on thegra-phi-te whichtis formed in the iron and induccs the foimation of typeA graphite. It also improves the matrix *of the iron produced.

The desulfurization which occurs in the cupola Well by reaction with.the finely divided calcium carbide in the stream ,of inert gas is farsuperior to the post-cupoia carbide injection procedure because in thelatter the calcum carbide, due to its low density, floats to the top ofthe iron whereit is admixed with slag and is in contact with the metaland the sultur therein for only, a short period of time. tOftentonly asurface melting reaction of the calcium carbide takes place and thedesulfurizing eitect is low. i

in the present invention the desul'furization is more effective thanthat obtained by adding calcium carbide to the cupola charge because inthat procedure the contact between molten metal and calcium ca rbide istransistory and incomplete. Furtherrnore, part of the calcium carbide isoxidized in the melting Zone above the tuyeres and is lost. In thepresent procedure, however, .the calcium carbide is completely contactedwith the iron and the d sulfurization efiect is much greater than inprior procedures. Furthermore, the introduction of calcium carbide tothe molten iron can he continue-d over the entire operation of thecupola. It is also possible to` carefully control the amount of calciumcarbide injected into .the moiten metal so a-s to obtain the maximum`desultu-rization eficiency.

The e procedure of this invention can be applied to molten iron inbothintermittently tapped cupolas and continuously taped cupolas. inintermittently tapped cupolas the iron is drawn oftfrom time to time(eg, every five t-o ten minutes) and the depth of the pool of molteniron varies.t Iust after tapping, the pool is at its minimum depth andmay be below the inlet for the stream of inert gas containing thecaicium carbide. During the period when the nolten metal is below the'inlet only the stream of inert gas is passed in; As the molten metalaccumulates in the well of the cupola and covers the inlet for theinertgas, the introduction of powdered calcium carbide on an ntermittentbasis is commenced. it desired, the carbide can be injectedona,continuous basis at a lower rate. The carbide injection is continueduntil the height of the molten metal pool reaches the slag hole 29* atwhich time slag begins to run off. At this point the cupola is againtapped and the metal pool is i'educed to its lowest level. g

With continuously tapped cupolas the molten metal is drawn Ott atapproximately the rate in which it is meited down in the cupola and thedepth of the melt in the cupola well is approximately constant. In suchcupolas it is important that the inlet ports through. which the ream ofinert gas hearing the powdered calciurn carbide is introduced, be at alevel below the minimum 'height of the pool of molten metal, therebyproviding for the introduction of the inert gas stream below the surfaceof the molten metal at all times. The introduction of powdered calciumcarbide into the inert gas stream is preferahly done on an ntermittentbasis to achieve maximum dispersion of the calcium carbide in the molteniron and improve the efficiency of the operation. With both types ofcupolas, it is importantlthat the gas stream be passed continuously intothe cupola in order to prevent pluggng of the inlet with metal or slagIt is advantageous to have several inlets into the cupola well toachieve maximum distribution of the calcium carbide throughout thernolten metal. C-rdinarily about tour inlets placed symmetricaliy aroundthe circumference'of the cupola below the level -of the molten metal aredesirable.

in the operation of the procedure of this invention, a flow rate ofapproximateiy 6 to 8 cubic feet of inert gas per minute at a pressure inthe range of 15 to 30 p.s.i.g. through each port is desirabie,althoughflow rates of 5 to 15 cubic feet per minute are satisfactory.?Calcium carbide in powdered form` (14 mesh or finer) is injected ,intothe gas stream for short periods of time and carried by the gas streaminto the ,molten iron. Ordinarily 5 to 10 pounds of' calcium carbideperton of iron is used in order to achieve satistactory desuifurization.i Two pounds` of calcium carbide is equivalent to one pound of sulfurcontained in the molten iron but ordinarily excesses of 50-100% areused. Generally about 8 to 10 pounds of calcium carbide are used perpound of sulfur removed from the iron. Ordinarily injection periods of-15 seconds are adequate, with periods of 5-15 seconds betweeninjections. However, injection periods up to one minute in duration withperiods up to one minute between injections are satisfactory. The totaltime of the periods of injection is controlled by the rate of injectionof the calcium carbide so that the appropriate amount of calcium carbideis injected into each pool of molten iron between tappings. Ordinarlythe total injection time is in the range of one to three minutes per tonof iron.

By this procedure, it is generally possible to reduce the sulfur contentof the molten iron in the cupola to about 50% of its normal value inperiods of 5 to minutes. In accordance with this invention, the iron iseficiently desulfurized during the melting operation in the cupola. Thiselminates the post-furnace treatment, thereby reducing time of theoperation and avoiding cooling of the metal in the ladle. Furthermore,the desulfurization operation is more efiicient by injecting the calciumcarbide into the molten metal in the cupola because the iron must gothrough the area in which the calcium carbide is injected in order to betapped out of the cupola, whereas in ladle desulfurization the calciumcarbide floats to the top of the molten iron and is ineficientlycontacted with the iron. The loss of calcium carbide by floating to thesurface does not occur to any sgnificant extent in the cupola and allthe calcium carbide remains in ntimate contact with the molten iron inthe cupola well.

The invention is illustrated in further detail by means of the followingOperating example. It will be understood by those skilled in the artthat various modifications ofvoperating conditions can be made withinthe disclosure of this specificati-on without departing from theinvention.

Example I A number 3 acid-lined cupola furnace was charged withsubsequent charges each consisting of 150 pounds of pg iron, 200 poundsof scrap return, 140 pounds of scrap iron, 50 pounds of scrap steel, 65pounds of coke and pounds of limestone. Prior to charging the furnace,the coke bed was gnited in its normal way and the coke -bed was burntin. Then normal cupola practice was followed thereafter.

The cupola was equipped with four graphite nlet tubes of one-half inchinside diameter and approximately 2 inches outside diameter. Thegraphite tubes were fitted closely into holes in the cupola shell andextended partway through the refractory lining of the cupola. graphitetubes connected to holes in the lning of onehalf inch diameter and aboutone and one-half inches The in length which lead to the cupola well. Thecalcium carbide (14 mesh) was injected at a rate of approximately 7pounds per ton of iron intermittently, with ten seconds' injection andten seconds between injections.

Malten iron was tapped intermittently in the transfer ladle of about 750pounds Capacity and this iron was then poured into smaller pouringladles. Metal from the first tap was used to preheat the ladles and wasthen pigged. Metal from the succeedng taps was poured into molds whichproduced castings. The following results were obtained:

Time After Tap 1 (Min) Tap No. Percent S ..t QQOONOUUPODNP* The ironproduced in normal cupola operation without calcium carbide injectionhad an average sulfur content of 0.075%. From the foregoing data, it isseen that the sulfur content of the base iron as tapped was decreasedfrom 0.075% to &044% on the average.

I claim:

1. Method of desulfurizing iron which comprises injecting eight to tenpounds of powdered calcium carbide per pound of sulfur removed from theiron intermittently into molten iron below the surface thereof in acontinuous stream of inert gas through a series of peripheral 'ports inthe well of a cupola while said molten iron is in the well of saidcupola.

2. Method of claim 1 wherein the inert gas is nitrogen at a flow rate inthe range of 5 to 15 cubic feet per minute.

3. Method of claim 2. wherein the powdered calcium carbide is injectedintermittently into the nitrogen stream for periods of 5 to seconds,with periods of 5 to 60 seconds between injection periods.

References Cited by the Examiner UNITED STATES PATENTS 1,977,428 10/34Cromwell -130 2,577,764 12/51 Hulme 75-58 2,803,533 8/57 Bieniosek etal. 75-53 2,855,336 10/58 Curry 75-130 2,870,004 1/59 Estes 75-512,9l8,365 12/59 Kanamori et al. 75-53 2,963,364 12/60 Crockett et al75-58 BENJAMIN HENKIN, Pr'mary Exam'ner.

1. METHOD OF DESULFURIZING IRON WHICH COMPRISES INJECTING EIGHT TO TENPOUNDS OF POWDERED CALCIUM CARBIDE PER POUND OF SULFUR REMOVED FROM THEIRON INTERMITTENTLY INTO MOLTEN IRON BELOW THE SURFACE THEREOF IN ACONTINUOUS STREAM OF INERT GAS THROUGH A SERIES OF PERIPHERAL PORTS INTHE WELL OF A CUPOLA WHILE SAID MOLTEN IRON IS IN THE WELL OF SAIDCUPOLA.